All steps in the nuclear fuel cycle
generate radioactive waste. In the front end of the cycle -- i.e. uranium
mining and enrichment -- the radioactivity in the waste consists only
of the naturally occuring elements in the original ore body. These elements
are mainly uranium and its daughter products. During reactor operation,
a wide spectrum of different radionuclides are generated by nuclear reactions
(mainly fission) in the fuel, as well as through neutron activation of
different elements in reactor core materials and in the water circulating
in the reactor vessel. The fate of the generated radionuclides is one
of the following:

Decay within the nuclear plant;

Release into the environment (only some gaseous
radionuclides and very small amounts of some other nuclides);

Recycling within the fuel cycle (uranium and
possibly plutonium if the spent fuel is reprocessed);

Storage and disposal as radioactive waste.

The terminology of low-, intermediate-
and high-level waste is used only to provide a broad categorisation of
radioactive waste. In contrast to high-level waste, low- and intermediate-level
waste generates only negligible amounts of heat due to radiation and does
not require cooling during storage. Low-level waste normally can be handled
without particular shielding, while intermediate-level waste might require
shielding and may contain significant amounts of long-lived radionuclides.

More than 95 per cent of the total
activity will be contained in the spent fuel, or the high-level waste
if the fuel is reprocessed. The rest will appear in a variety of low-
and intermediate-level waste (L/ILW) generated during the day-to-day operation
of nuclear reactors, storage facilities and reprocessing plants (back-end
of the cycle).

This is a simplified description and
the details, nuclide by nuclide, are certainly more complicated. Factors
like reactor type and mode of operation of the nuclear plant, the treatment
of the spent fuel and the waste handling and conditioning itself will
all have an influence on determining which radionuclides are generated,
the amount produced and the type of radioactive waste in which they will
appear.

II. What are the types of radioactive waste?

Mill
tailings

The radioactive mill tailings from
uranium mining are by far the most voluminous radioactive waste generated
within the whole fuel cycle (50-100 times more by volume than all other
radioactive waste). They are normally stabilised and disposed of at or
close to the mine of origin. As these wastes contain natural long-lived
radionuclides, they must be disposed of in a way that affords long-term
protection to man and his environment. These questions are not dealt with
further in this issue brief, which is limited to a discussion of the disposal
of low- and medium-level waste containing artificially generated radionuclides.

Reactor waste

During reactor operation, L/ILW is
generated both as a liquid and as a solid. The liquid is contaminated
water from different parts of the reactor system and from the plant. Purification
or concentration of this water gives rise to slurries that are mixed with
cement or asphalt to form a stable waste form.

The solid waste is any potentially
radioactive material, such as filters, valves, pipes, trash, etc, from
the reactor systems or the plant. Most of the solid waste is generated
during maintenance and repair work. It is compacted, incinerated or simply
packed in drums. Embedding and/or encapsulation in concrete are methods
sometimes used to obtain stable waste packages.

Reprocessing waste

During reprocessing, the spent fuel
is dissolved and uranium and plutonium are separated for recycling. The
main waste product is the heat-generating high-level waste solutions containing
the bulk amount of fission products from the spent fuel. Some of the reprocessing
waste contains substantial amounts of long-lived radionuclides, so-called
alpha-waste or transuranic (TRU)-waste, and these will require the same
degree of isolation from man's environment as high-level waste or spent
fuel.

L/ILW is also generated at a reprocessing
plant. The treatment options are the same as for reactor waste: solidification
of slurries in cement or asphalt, compaction, incineration or packaging/encapsulation
of solid waste.

Decommissioning waste

The decommissioning and dismantling
of nuclear installations will also generate radioactive waste. In addition
to the same types of waste produced during plant operation, other types
of waste will be generated, notably some bulky internal structures from
the reactor, the reactor vessel and its surrounding concrete structure.

Other types of low- and intermediate-level
waste

Nuclear research, industrial and medical
uses of radionuclides also generate L/ILW. In countries with no nuclear
power programme, this constitutes the main category of radioactive waste,
while for countries with a nuclear programme, it represents only 5-30
per cent of the total volume of radioactive waste. In countries with nuclear
weapons, significant amounts of L/ILW as well as high-level waste are
generated by the military programmes.

The amount of radioactive waste
remaining after treatment will increase in years ahead because of the
continuing development of nuclear power for electricity production. Quantities
shown here should be used for trend purposes only, since waste quantities
can vary significantly depending upon the underlying assumptions used
to determine the amounts generated per installed 1000 megawatts of electric
power.

III. How is the waste handled?

L/ILW is normally conditioned and packaged
in drums or other containers at the site where it is generated. In some
cases, however, some types of waste are transported to a central treatment
facility. In certain countries, for instance, low-level burnable waste
is incinerated at a central site.

The chemical and physical properties
of the waste are essential for their management. Basically two major factors
must be considered in the classification of waste for its further handling,
storage, transportation and disposal. They are:

The level of radiation emitted by the waste,
and

The content and half-life of major radionuclides,
in particular the level of long-lived radionuclides in the waste.

Compared to the total amount
of toxic waste that has to be handled by society, the volume of radioactive
waste is still small. (The figure is based on data within the OECD/NEA
and the OECD Environment Directorate. It only gives a rough indication
of the relative order of volumes.)

The level of radiation will govern
the need for additional radiation shielding during handling, storage and
transportation and there are established international guidelines to be
followed. The content of long-lived radionuclides will determine the type
of long-term isolation required for disposal of the waste.

IV. What waste disposal methods are used?

With the exception of sea dumping,
which relied largely upon dilution and dispersion in the environment,
but is now suspended, all disposal concepts for L/ILW rely on isolation
from the biosphere at least initially and until radioactive decay has
made subsequent releases to the environment compatible with radiation
protection criteria. Multi-barrier containment systems have been designed
for this purpose and most countries have already defined and sometimes
implemented disposal practices and policies.

The length of the isolation period
required is governed by the radiotoxic properties of the waste and particularly
the half-lives of the radionuclides contained. A surface or near-surface
facility is usually regarded as suitable for short-lived, low-level waste,
provided some form of site surveillance is maintained after closure of
the site, notably to prevent intrusion by man. However, it is clearly
recognised that the maintenance of institutional control (i.e. any form
of surveillance by man carried out on a continuous basis under the supervision
of the responsible regulatory authorities) cannot be relied upon beyond
a limited time period and a maximum of 300 years is usually regarded as
a prudent limit in this respect. This results in a clear requirement for
surface and near-surface disposal facilities: the waste they can accept
should be such that the site could be released for unrestricted use, e.g.,
roads, houses or even farming, at the end of the agreed institutional
control period.

In contrast, deep geologic isolation
as a totally passive system is considered necessary for long-lived waste.
In this case, institutional control measures would not be needed in the
far future to preserve the long-term integrity of a well-selected site
because the probability of interference by natural events and human actions
is very limited. This reasoning, however, does not exclude the possibility
of deep geological disposal for short-lived waste, which would make institutional
control superfluous from a strict safety viewpoint.

Actual practice

In practice, the main policies followed
for the disposal of low- and intermediate-level waste are:

Near-surface disposal, which is particularly
valid for relatively large nuclear power programmes which produce considerable
volumes of LLW. France, the United States, and the United Kingdom already
have such facilities in operation for short-lived waste.

Geologic disposal, which has the advantage of avoiding
the need to separate short- and long-lived radioisotopes before disposal,
as in the case of shallow-land burial. Disposal in various abandoned
mines or specially constructed caverns is carried out or planned, notably
in Finland, the Federal Republic of Germany, Sweden, Switzerland and
the United Kingdom.

France's first surface repository,
the "Centre de la Manche", has been in operation since 1969 in a 12 hectare
area located at the western tip of the Cotentin Peninsula, close to the
La Hague reprocessing plant. The total capacity of this centre is about
500 000 m3 of waste and up to now, it has received about 400 000 m3 of
waste. The centre will be filled completely at the beginning of the 1990s.
It is planned to start operation of a new disposal facility, Centre de
l'Aube in north-eastern France, by early 1991. The disposal capacity will
be 1 million m3 of waste.

The Swedish repository for low-level
waste, SFR, is located in the bedrock below the Baltic Sea close to the
Forsmark nuclear power plant, north of Stockholm. The facility, excavated
rock caverns and a silo, is accessible through tunnels from the coast.
The bedrock cover from the top of the caverns to the sea is 60 m. Operation
of SFR began during 1988. The capacity in the first phase is 60,000 m3
of waste and in total it is planned to dispose of about 100,000 m3 of
waste, which is the projected total amount of low-level waste produced
until the year 2010 by the Swedish nuclear power programme.

V. How are the disposal costs financed?

The "Polluter Pays Principle" is widely
applied for radioactive waste disposal, sometimes including R&D activities.
This principle is incorporated in national laws, for example in Belgium,
Finland, France, the Federal Republic of Germany, Spain, Sweden and the
United States. On this basis, financing of radioactive waste disposal
may take different forms, such as advance contributions from waste producers
according to waste production and expenditure estimates, provisional or
final fees at the time of waste delivery, fees on nuclear electricity
production, and contribution to waste management funds. Decommissioning
funds are also sometimes used to cover the disposal of decommissioning
waste. Given the relatively low cost of L/ILW waste disposal (up to a
maximum few per cent of the cost of nuclear electricity) and the specific
financing arrangements already made at the national level, there is apparently
no fundamental difficulty in this respect, even if disposal is considerably
delayed.

VI. What measures are taken to ensure the
safe disposal of L/ILW?

In all countries the siting, construction,
operation and closure of a radioactive waste repository is subject to
an extensive licensing and control procedure. There is also a control
at the source of the waste production (nuclear facilities, R&D establishments,
radioisotope production and application facilities, hospitals, etc.) and
the radioactive substances are recorded and surveyed throughout handling,
transport and storage operations. These bookkeeping procedures normally
ensure that all the waste generated is actually controlled and cannot
be disposed of outside the agreed system.

For disposal of waste at a repository,
quantitative waste acceptance criteria have to be met. These criteria
may concern:

Limits on the concentration of radionuclides
in wastes,

Limits on the total activity of radionuclides
to be disposed of at a given facility,

Such criteria will, to a large extent,
be based on international and national radiological protection standards
but the actual quantitative criteria will also depend upon the type of
site and repository in each case.

A detailed characterisation of the
site is made before proceeding to final site selection and construction
of the repository. It includes, for instance, measurements and modelling
of the general geological characteristics of the site, the groundwater
movements and the geochemical conditions. The repository design, in many
cases, includes additional engineered barriers like thick concrete vaults
and backfilling by dense clay. These will enhance the protection against
excessive or premature groundwater intrusion to the waste and will minimise
and delay radionuclide transport from the waste to the environment.

The long-term safety of L/ILW disposal
can be systematically assessed through predictive modelling of gradual
failure of the engineered barriers, i.e., the waste form, waste package
and the backfill (if any) and the potential subsequent transport to man's
environment of radionuclides by circulating groundwater. A complete safety
assessment will also include an analysis of the potential effects of disruption
of the repository by geological and environmental changes, e.g., faulting
or glaciation, as well as human intrusive actions at the site, e.g. drilling
or living at the site. During the licensing procedure, the results of
the safety analysis and their inherent uncertainties will be checked and
assessed by the regulatory authorities.

During construction, operation and
closure of a repository, strict control will be exercised to ensure that
the disposal is implemented according to the plans.

VII. What is the role of the OECD Nuclear
Energy Agency?

The NEA has always been concerned with
the problem of radioactive waste disposal and for the past 15 years, this
has been a priority area. Its principal role is to assist its Member countries
in the further development of methodologies to assess the long-term safety
of radioactive waste disposal systems and to increase confidence in their
application and results. This is done through the exchange of information
and experience among national experts, and by joint studies of issues
important for safety assessment (identification of potentially disruptive
events, treatment of uncertainties). Related computer codes (in particular
for probabilistic events) and data bases (used to assess the behaviour
of radioactive materials in the geosphere) are developed and validated
at an international level.

These activities form part of an integrated
international effort to reach the level of scientific understanding needed
to ensure that nuclear waste disposal systems will be able to contain
and isolate the radioactive materials so that no harm will be caused to
man or his environment either now or in the future. Such co-operative
programmes also enhance confidence in the quality of the safety analyses
upon which the acceptability of nuclear waste disposal is to be judged.

Although the NEA activities in this
area are primarily focussed on deep disposal of high-level, long-lived
radioactive waste, many of the results are equally valid for the disposal
of low-level waste. In addition, there are regular activities directly
related to questions concerning low-level waste, for example, studies
of how to estimate radionuclide content in the wide range of low-level
waste and a recent workshop on assessment of repositories for low-level
waste.

From 1967 to 1982, sea-dumping operations
for radioactive waste were carried out in the North-East Atlantic under
the supervision of NEA. Up to 8 NEA countries participated in these operations.
However, since 1983 there has been a non-binding moratorium on the sea-dumping
of radioactive waste. A co-ordinated Research and Environmental Surveillance
Programme (CRESP) was set up in 1980 and continues to operate, mainly
to collect scientific information on the Atlantic disposal sites.

REFERENCES

Objectives, Concepts and Strategies for the
Management of Radioactive Waste Arising from Nuclear Power Programmes,
Report by an NEA Group of Experts, OECD/NEA, Paris, 1977.

Technical Appraisal of the Current Situation
in the Field of Radioactive Waste Management--A Collective Opinion by
the Radioactive Waste Management Committee, OECD/NEA, Paris, 1985.